1. Field of the Invention
The present invention relates to a process for the preparation of 7-oxo-7H-dibenzo-[d e,h] -quinolin-2-ol (I), a known compound also known as 1-aza-2-hydroxy-benzanthrone.
2. Prior Art
The known compound, 1-aza-2-hydroxy-benzanthrone (I) is a useful intermediate for the synthesis of dyestuffs. Thus, for instance, starting from that compound, and by operating according to the procedures described in Italian Pat. Nos. 869,691 and 901,929, excellent vat dyes are obtained, these dyes having color hues ranging from brilliant blue to violet blue. These dyes belong to a new series of dyes based on 5,14-diaza-isoviolanthrone, which is structurally similar to isoviolanthrone but which have application characteristics, which for purity of tone are much superior, particularly for the exceptional chlorine resistance.
Compound (I), i.e., 1-aza-2-hydroxy-benzanthrone, may also be used in the preparation of azoic dyes, since it is able to couple in the 3-position ortho with respect to the OH group.
Italian Pat. No. 860,016, discloses a method for the preparation of 7-oxo-7H-dibenzo[d e,h]-quinolin-2-ol by reacting 1,4-naphthoquinone and methyl hexadienoate, to form the intermediate adduct, methyl 1-(1,1a,4,4a-tetrahydro-anthraquinone)-acetate, which after treatment with ammonia and subsequent dehydrogenation and cyclization in the presence of air and KOH, leads to compound (I).
Italian Patent Application 26722 A/73, by Montedison S.p.A., filed on July 18, 1973 discloses a process for the preparation of compound (I) wherein an alkyl ester of anthraquinone-1-acetic acid is directly reacted with ammonia in hydroxylated solvents, preferably methanol, in the presence of a strong base and/or a reducing agent according to the reaction scheme: ##STR1## wherein R is an alkyl group having from 1 to 5 carbon atoms. These known techniques are not, however, related to the process of the present invention.